1. Technical Field
The present invention relates to an austenitic light-weight high-strength steel, and more particularly, to an austenitic light-weight high-strength steel with excellent properties of welds, and a method of manufacturing the same.
2. Description of the Related Art
Recently, greenhouse gas emission regulation policy has been reinforced as an interest in environmental pollution is globally increased. In addition, in accordance with demand of consumers for improving fuel efficiency according to an increase in oil price, demand for developing light-weight steel material has been increased.
In accordance with the demand, in the steel industry, TWin Induced Plasticity (TWIP) steel was developed by adding a large amount of aluminum (Al) which is a light-weight element relative to the existing steel material, for weight lightening. However, when aluminum (Al) has an amount of 5 wt % or more in the TWIP steel, the TWIP steel has a limitation in weight lightening since stacking fault energy of the steel is increased to inhibit twin deformation.
Meanwhile, as a high-aluminum light-weight steel including aluminum having an amount of 5 wt % or more, austenitic steel is a representative example.
The austenitic steel is generally classified into austenitic steel consisting of austenite, ferrite, and carbides and austenitic steel consisting of austenite and carbides. Among them, the austenitic steel consisting of austenite, ferrite, and carbides has a problem with deterioration in elongation according to the presence of ferrite, and the austenitic steel consisting of austenite and carbides has a problem with deterioration in properties of welds according to austenite crystal grain growth despite excellent properties of a basic material.
As a document regarding the present invention, Korean Patent Laid-Open Publication No. 10-2014-0085088 (Jul. 7, 2014) discloses a high specific strength steel sheet with excellent ductility and a method of manufacturing the same.
The Patent document describes a steel sheet including 0.15 wt % to 0.5 wt % of C, 6.0 wt % to 8.0 wt % of Mn, 5.0 wt % to 6.0 wt % of Al, 0.05 wt % to 0.5 wt % of Si, less than 0.02 wt % of S, and a remaining amount of Fe and other unavoidable impurities, wherein yield strength is 600 MPa or more, and a value obtained by multiplying tensile strength and elongation is 28,000 MPa·% or more.
However, this steel sheet has a limitation in weight lightening since the maximum amount of aluminum (Al) is merely 6 wt %, and has difficulty in securing sufficient fraction of austenite since the maximum amount of manganese (Mn) is also merely 8 wt %.